Steam turbines are used for many types of drive as prime movers. Drives include, but are not limited to, propulsion systems, generation of electricity, pumps and compressors. A ship propeller is one form of propulsion that can be driven by steam turbines.
While steam turbines can be in many shapes and forms, steam turbines all have some common elements. The steam turbine has a moving set of blades attached to a shaft to transmit the power. A set of stationary blades or nozzles are used to direct the steam towards the rotor or moving blades, where the blades are attached to the shaft. The two sets of blades are referred to together as a stage.
In one of several steam turbine designs, the first stage, the first set of stationary blades and the first set of rotor or moving blades, acts as an impulse stage in which the pressure of the steam drops as the steam passes through the stationary blades and remains relatively constant as the steam passes through the moving blades. As the pressure drops, the velocity of the steam increases as the steam passes through the stationary blades. The velocity of the steam decreases as the rotor blades transmit the energy to rotate the shaft.
The process of decreasing pressure to control or limit flow of steam or fluid is called throttling. The process of throttling results in a loss of energy. One of the factors in determining the amount of energy loss is how well a control or throttle valve is tailored to the amount of flow required to produce normal power versus the flow required to produce maximum power. Typically the valve is designed for the maximum fluid flow that is required by the steam turbine or other power producing device. As the amount of fluid (steam) which is flowing at one time through the valve is decreased, the throttling losses increase.
To increase the efficiency in throttling of the steam turbine, inlet valves are configured as multiple valves which are opened sequentially. Each of the valves are open such that only one valve is partially open. (i.e., the other valves are completely closed or completely open.) Each valve directs the flow of steam to a portion of the entire arc, for example six (6) valves each would direct flow to 60 degrees of the 360 degree full-arc of the turbine. If the turbine was running at 70 percent power, four valves are open completely, one valve is closed and the sixth is partially open. In practice, the power produced, or steam flow through the valves may not be proportional to the number of valves open.
It is recognized that the introduction of steam in a segment of the arc and not in the entire arc, results in a phenomenon which causes greater stimulus on the first stage buckets or blades and higher radiated noise. However, a single valve turbine which introduces fluid to the entire arc results in inefficiencies due to throttling losses of the valve.
The invention relates to a steam turbine which has multiple valves for introducing steam into a steam turbine. Each of the input valves introduce steam flow around the entire 360 degree arc. A uniform flow is introduced completely around the shaft and to the moving blades. The set of nozzles (stationary blades) are each divided into a plurality of circumferential chambers in a axial flow turbine and a plurality of axial chambers in a radial flow turbine.
Each set of chambers extends around the full arc of the turbine. Each set has a valve for controlling the flow of steam into the respective chamber. The chambers are designed so that all valves are open when the turbine is running at maximum output. The chambers are sized such that each valve is either open or closed when the turbine is at its normal or reduced output operating condition. For example, if the steam turbine is typically operated at 65 percent power output, and has two chambers, one chamber and its controlling valve would be sized to provide the steam flow required to produce 65 percent power, and the second valve and chamber sized to provide the additional flow to produce the remaining 35 percent power. The valve of the first chamber would be open and the valve of the second chamber would be closed during normal 65 percent power operation.